The corpus tests interleaved hand-written content (test cases) with
generated content (printed ASTs).
This made merge conflicts hard to resolve because you can't just
regnerate the printed ASTs without potentially throwing away new test
cases that came from either branch (or depending on whether the merge
conflict markers appeared, the corpus test could be ruined completely).
The old design did have one nice advantage: Reviewers could see the
printed ASTs alongside the source code from which it was generated.
To preserve this feature, the source code for the test case is itself
included in the generated output file.
